A standard system for making fiber- or chip-board, e.g. OSB or MSB panels, has as described in German patent documents 102 22 969 and 102 22 970 of R. Burckhardt a multistory press that is loaded by a conveyor system with a stack of screens on which have been formed respective uniform but loose mats of the material that is to be pressed into a panel by the press. This material is normally wood chips and/or fibers mixed with an appropriate heat-setting binder, e.g. a phenolic resin, so that, when the mat is pressed and heated, a rigid panel suitable for structural use is formed.
The fiber or chip mats are formed on screens each normally constituted as a flexible but strong rectangular mesh panel having a stiffening bar along leading and trailing edges. The conveyor normally has a pair of endless belts or chains that are spaced horizontally from each other and that are each provided with a succession of grabs or hooks adapted to hold ends of the stiffening bars, operating so as to hold the screens so they are taut and planar. The endless conveyor chains have a generally horizontal upper stretch extending in a horizontal transport direction from a mat forming station at an upstream end, through a press loader, then through the press, then through a press unloader to a downstream end. From the downstream end the conveyor has a return stretch that passes back in an upwardly concave arcuate path in a return direction opposite the transport direction underneath the press to the upstream end. The press stands on the floor and a well or pit is formed underneath it for the return stretch.
Thus a mat is formed on each of the screens as it passes underneath the mat former at the upstream end of the transport stretch. The screens are then separated from the conveyor at the press loader and put in a rack upstream of the multistory press. Periodically the screens in the loader rack are moved as a batch into the multistory press for compression into finished panels, although the system can operated with a simple single-story press. The finished panels and their screens are moved as a batch out to the unloader and refitted to the conveyor for movement away from the press. Finally the panels are stripped off the screens and the empty screens are recirculated back underneath the press to the upstream end to restart the cycle.
Such a system is extremely effective in that it can convert bulk material—wood chips or fibers or plastic particles——into rigid panels at a very high production rate. The conveyor runs continuously, with the batch operation of the press being accommodated by the press loader and unloader, for a very high production rate.
A problem with such an operation is that the screens are subject to considerable wear and must be replaced if they become damaged, since they will leak particles so as to produce a bad finished product and foul the equipment. Accordingly, above-cited German '969 provides near the downstream end of the press along the return stretch of the conveyor a system for removing damaged screens and replacing them with good ones. The problem with such an arrangement is that it requires that the well under the press through which the conveyor returns be substantially enlarged to accommodate the screen-changing unit, as the screens measure several meters in length and width, e.g. 14 m long, and can weigh as much as 350 kg, although they can be rolled up when not being used. Hence these systems add considerably to the installation costs for a panel-making system.